Four explorers are summoned to Peru by the brilliant physicist Dr Thorkel. They discover a rich source of radium and a half-mad Thorkel who shrinks them down to one-fifth their normal size when they threaten to stop his unorthodox experimentation.

• Paramount Pictures
• Albert Dekker
• Thomas Coley
• Janice Logan
• Charles Halton
• Victor Kilian
• Frank Yaconelli
• Paul Fix
• Frank Reicher